Apparatuses including a rotor group and methods of damping the apparatuses

ABSTRACT

An apparatus includes a rotor group rotatable within the apparatus and a bearing assembly supporting the rotor group. A support structure supports the bearing assembly and is fixed in the apparatus. The support structure includes a support housing, an anisotropic support that engages the bearing assembly and the support housing, and a squeeze film cavity that is defined between the anisotropic support and the support housing. A damper fluid supply line is in fluid communication with the squeeze film cavity. A fluid interruption device is disposed in the damper fluid supply line. A method of damping the apparatus includes supplying fluid under pressure to the squeeze film cavity through the damper fluid supply line. Upon surpassing a predetermined value of a variable correlated to rotational speed of the rotor group, the fluid flow to the squeeze film cavity is interrupted with the fluid interruption device.

TECHNICAL FIELD

The present invention generally relates to apparatuses including a rotorgroup and methods of damping the apparatuses, and more particularlyrelates to apparatuses and methods in which the rotor group is dampedthrough squeeze film damping.

BACKGROUND

A gas turbine engine may be used to power various types of vehicles andsystems. A particular type of gas turbine engine that may be used topower aircraft is a turbofan gas turbine engine. A turbofan gas turbineengine may include, for example, five major sections, a fan section, acompressor section, a combustor section, a turbine section, and anexhaust section. Each section includes rotating components that arecoupled to a rotor. The rotating components may be coupled togethereither by a tie shaft or bolted flange joints to form a rotor group. Twoor more bearing assemblies may be employed to support the rotor group.Generally, the bearing assemblies may be surrounded by a supporthousing, which may be connected to an engine case.

During engine operation and high-speed rotation of the rotor group,vibration may occur when the rotor group rotates. Typically, thevibration is caused by a rotating mass imbalance, or may occur when aradial deflection of the rotor results in tangential force normal to thedeflection. For some rotor groups, this tangential force excites afundamental mode of the rotor and creates a non-synchronous vibration(NSV). The magnitude of the tangential force increases with thedeflection, resulting in high bearing loads that become unstable andcause damage to the gas turbine engine. A damping system is typicallyrequired in the engine to reduce vibration, especially around a criticalspeed of the rotor group, thereby minimizing bearing loads andsafeguarding against potential damage to the bearing assemblies andsupports that can be caused by the unstable vibration.

One example of a damping system that is known for use in gas turbineengines is a squeeze film damper. A squeeze film damper operates bysupplying fluid (usually oil) into a squeeze film cavity formed via aclearance between the support housing and the bearing assemblies. Thefluid in the squeeze film cavity is under pressure and damps vibrationof the rotor through viscous resistance thereby exerting a damping forceon the bearing assembly. Squeeze film dampers are particularly effectivefor damping synchronous vibration of the rotor group that occurs at thecritical speed.

Although squeeze film dampers are relatively useful in reducingsynchronous rotor vibration, they may suffer drawbacks. For example,squeeze film dampers are generally effective for damping rotor vibrationat a critical speed of the rotor group, where vibration is greatest andwhere damping is most desired. The critical speed of the rotor group ingas turbine engines is generally relatively low within a range ofrotational operating speeds of the gas turbine engines, and the criticalspeed of the rotor group is often traversed during normal operation ofthe gas turbine engines. The fluid in the squeeze film damper generallycontinues to be under pressure once the critical speed is traversed.However, once the critical speed is traversed, synchronous vibration isless than at critical speeds and the need for damping the synchronousvibrations is greatly reduced. Further, damping may even be undesirableonce the critical speeds are traversed because the damping force exertedby the pressurized fluid in the squeeze film damper combines withelastic force to create excessively high bearing loads, which leads toexcessive engine vibration. For example, as shown in FIG. 1, continueddamping after traversing the critical speed, while initially decreasingan amplitude of bearing load, causes an increase in bearing load andattendant system vibration at higher rotational operating speeds of therotor group. Many gas turbine engines that employ squeeze film dampersdo not cut off a fluid flow to the squeeze film damper once the criticalspeed is traversed because cutting off the fluid flow to the squeezefilm damper invites NSV, which causes the aforementioned problems.

Accordingly, it is desirable to provide apparatuses including a rotorgroup that can be damped to minimize bearing loads around a criticalspeed of the rotor group, but that also exhibits minimized bearing loadsupon traversing the critical speed. In addition, it is desirable toprovide methods of damping vibration in such apparatuses both around thecritical speed of the rotor group and once the critical speed istraversed. Furthermore, other desirable features and characteristics ofthe present invention will become apparent from the subsequent detaileddescription of the invention and the appended claims, taken inconjunction with the accompanying drawings and this background of theinvention.

BRIEF SUMMARY

Apparatuses and methods of damping the apparatuses are provided. In anembodiment, an apparatus includes a rotor group that is rotatable withinthe apparatus and a bearing assembly that supports the rotor group. Asupport structure supports the bearing assembly and is fixed in theapparatus. The support structure includes a support housing, ananisotropic support that engages the bearing assembly and the supporthousing, and a squeeze film cavity that is defined between theanisotropic support and the support housing. A damper fluid supply lineis in fluid communication with the squeeze film cavity for independentlyproviding a fluid to the squeeze film cavity. A fluid interruptiondevice is disposed in the damper fluid supply line for interrupting afluid flow to the squeeze film cavity.

In another embodiment, an apparatus includes a rotor group that isrotatable within the apparatus and a bearing assembly that supports therotor group. A support structure supports the bearing assembly and isfixed in the apparatus. The support structure includes a supporthousing, an anisotropic support that engages the bearing assembly andthe support housing, and a squeeze film cavity that is defined betweenthe anisotropic support and the support housing. The anisotropic supportincludes at least two rings that are connected byasymmetrically-arranged beams. A damper fluid supply line is in fluidcommunication with the squeeze film cavity for independently providing afluid to the squeeze film cavity. A fluid reservoir is in fluidcommunication with the damper fluid supply line for providing the fluidto the damper fluid supply line. A main supply line is disposed betweenand in fluid communication with the fluid reservoir and the damper fluidsupply line, and the damper fluid supply line is split from the mainsupply line. A bearing fluid supply line is further split from the mainsupply line for independently providing the fluid to the bearingassembly. A fluid interruption device is disposed in the damper fluidsupply line and controlled by an engine control system for interruptinga fluid flow to the squeeze film cavity. The fluid flow to the bearingassembly is uninterrupted when the fluid flow to the squeeze film cavityis interrupted by the fluid interruption device.

A method of damping vibration in an apparatus includes providing theapparatus including a rotor group that is rotatable within the apparatusand a bearing assembly that supports the rotor group. A supportstructure supports the bearing assembly and is fixed in the apparatus.The support structure includes a support housing, an anisotropic supportthat engages the bearing assembly and the support housing, and a squeezefilm cavity that is defined between the anisotropic support and thesupport housing. A damper fluid supply line is in fluid communicationwith the squeeze film cavity for independently providing a fluid to thesqueeze film cavity. A fluid interruption device is disposed in thedamper fluid supply line for interrupting a fluid flow to the squeezefilm cavity. The method further includes supplying fluid under pressureto the squeeze film cavity through the damper fluid supply line. Uponsurpassing a predetermined value of a variable correlated to rotationalspeed of the rotor group, the fluid flow to the squeeze film cavity isinterrupted with the fluid interruption device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 is a graph showing bearing loads, in pounds-force, as a functionof rotational speed of a rotor group within an apparatus as shown inFIG. 2 when a squeeze film damper is employed with fluid in the squeezefilm damper pressurized at all rotational speeds;

FIG. 2 is a partial cross-sectional side view of an apparatus includinga rotor group, a bearing assembly, and a support structure including ananisotropic support in accordance with an exemplary embodiment;

FIG. 3 is a perspective view of the anisotropic support of FIG. 2; and

FIG. 4 is a graph showing bearing loads, in pounds-force, as a functionof rotational speed of the rotor group within the apparatus as shown inFIG. 2 when a squeeze film damper is employed with fluid in the squeezefilm damper interrupted once a rigid body critical speed of the rotorgroup is interrupted.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding background or the following detaileddescription.

Apparatus and methods of damping vibration in the apparatuses areprovided herein. In particular, the apparatuses may be further definedas gas turbine engines and include a rotor group, a bearing assembly,and a support structure including a support housing, an anisotropicsupport, and a squeeze film cavity defined between the anisotropicsupport and the support housing. When filled with pressurized fluid, thesqueeze film cavity functions as a squeeze film damper. The apparatusesand methods employ damping from both the squeeze film damper and theanisotropic support in a way that minimizes bearing loads both around arigid body critical speed of the rotor group and once the rigid bodycritical speed is traversed to thereby minimize vibration of theapparatuses in a range of rotational operating speeds of the rotorgroup. In particular, fluid is supplied under pressure to the squeezefilm cavity, and a fluid flow to the squeeze film cavity is interruptedupon surpassing a predetermined value of a variable that is correlatedto rotational speed of the rotor group, representing traversal of therigid body critical speed of the rotor group or a speed at which dampingwith the squeeze film damper begins to create increasing bearing load.Once the fluid flow to the squeeze film cavity is interrupted, thesqueeze film damper effectively ceases damping, thereby reducing thevibration of the rotor group. However, there is a possibility ofnon-synchronous vibration (NSV) arising once hydraulic damping from thesqueeze film damper is ceased. To dampen the NSV, the anisotropicsupport is present and provides cross-couple stiffness to protect therotor group against tangential excitation that creates the NSV. In thismanner, high bearing loads attributable to the squeeze film damper atrotational speeds above the rigid body critical speed are minimized,thereby minimizing vibration of the apparatus below vibration that wouldotherwise be experienced with continued damping by the squeeze filmdamper.

An exemplary embodiment of an apparatus 10 and a method of dampingvibration in the apparatus 10 will now be addressed with reference toFIG. 2. As shown in FIG. 2, the apparatus 10 is a gas turbine engine,such as an engine of an aircraft. However, it is to be appreciated thatthe apparatuses described herein are not limited to gas turbine enginesonly and can include any apparatus 10 having a rotor that would benefitfrom damping of vibration at critical speeds and after traversing thecritical speeds.

The apparatus 10 includes a rotor group 12 that is rotatable within theapparatus 10. The rotor group 12 refers to a rotor 14 and any rotatablefeatures within the apparatus 10 that are fixed relative to the rotor14. A bearing assembly 16 supports the rotor group 12 within theapparatus 10. In particular, the bearing assembly 16 engages the rotor14 to support the rotor group 12. Although only a single bearingassembly 16 is shown in FIG. 2 for simplicity of illustration, it is tobe appreciated that a plurality of bearing assemblies 16 may be includedto support the rotor group 12. The bearing assembly 16 includes bearingelements 18 and an inner race 20 that is fixed on the rotor 14 and thatprovides a contact surface 22 for the bearing elements 18. The innerrace 20 is also configured to confine the bearing elements 18 within theinner race 20.

A support structure 24 supports the bearing assembly 16 and is fixed inthe apparatus 10, i.e., the support structure 24 does not rotate duringoperation of the apparatus 10. When the plurality of bearing assemblies16 is included, each bearing assembly 16 may have its own correspondingsupport structure 24. The support structure 24 promotes axial rotationof the rotor 14, and by extension the rotor group 12, about an idealaxis during rotation of the rotor group 12 by supporting the rotor 14through the bearing assembly 16. By promoting axial rotation of therotor 14, vibration of the apparatus 10 is minimized that can resultfrom rotation of the rotor 14 about an axis other than the ideal axis ofrotation due to synchronous and non-synchronous vibration experienced bythe rotor group 12. The support structure 24 includes a support housing26. The support housing 26 is fixed to another non-rotating structure 30of the apparatus 10 and is fixed to the non-rotating structure 30 of theapparatus 10, for example, through a flange and bolt connection.

The support structure 24 further includes an anisotropic support 28 thatengages the bearing assembly 16 and the support housing 26. Inparticular, the anisotropic support 28 engages the bearing elements 18of the bearing assembly 16 and provides an outer race 32 that, incooperation with the inner race 20, holds the bearing elements 18 inplace. The anisotropic support 28 provides support anisotropy, ordirectionally-dependent, stiffness to the rotor 14 through directlyengaging the bearing elements 18, and the anisotropic support 28 iseffective for neutralizing non-synchronous vibration of the rotor group12 during rotation. In the embodiment shown in FIG. 2, and as best shownin FIG. 3, the anisotropic support 28 includes at least two rings 34, 36that are connected by asymmetrically-arranged beams 38, with theasymmetric arrangement of the beams 38 providing anisotropy to theanisotropic support 28. In this embodiment, one of the at least tworings 36 provides the outer race 32 on an inner surface thereof, andanother of the at least two rings 34 provides an inner-circumferentialattachment flange 40 for facilitating attachment of the anisotropicsupport 28 to the apparatus 10. In particular, the anisotropic support28 can be bolted to the support housing 26 through theinner-circumferential attachment flange 40.

A squeeze film cavity 42 is defined between the anisotropic support 28and the support housing 26 of the support structure 24. In particular,in the embodiment of FIG. 2, the squeeze film cavity 42 is definedbetween one of the at least two rings 36 of the anisotropic support 28,on an outer surface 44 thereof directly opposite the outer race 32, andthe support housing 26. In an embodiment, the squeeze film cavity 42extends circumferentially and continuously about the anisotropic support28; however, it is to be appreciated that configurations are possible inwhich additional features (not shown) are designed into the squeeze filmcavity 42 that interrupt continuous circumferential extension of thesqueeze film cavity 42. As also shown in the embodiment of the apparatus10 of FIG. 2 and the anisotropic support 28 of FIG. 3, the anisotropicsupport 28 includes two grooves 46 that receive piston rings 48, withthe piston rings 48 further defining and sealing the squeeze film cavity42.

A damper fluid supply line 50 is in fluid communication with the squeezefilm cavity 42 for independently providing a fluid to the squeeze filmcavity 42. In particular, the damper fluid supply line 50 provides fluidonly to the squeeze film cavity 42 or, when the plurality of bearingassemblies 16 and corresponding support structures 24 are included, toeach squeeze film cavity 42. In the embodiment of FIG. 2, the damperfluid supply line 50 is incorporated into the support housing 26 with afluid inlet 52 to the squeeze film cavity 42 defined in the supporthousing 26 adjacent to the squeeze film cavity 42. However, in otherembodiments (not shown), it is to be appreciated that a portion of thedamper fluid supply line 50 may be disposed outside of the supporthousing 26.

In accordance with the exemplary method, fluid is supplied underpressure to the squeeze film cavity 42 through the damper fluid supplyline 50. The squeeze film cavity 42, when filled with fluid underpressure, functions as a squeeze film damper and is effective fordamping vibration of the rotor group 12 during rotation. In particular,the squeeze film damper is effective for damping synchronous vibrationof the rotor group 12, especially at and around a critical speed of therotor group 12 where synchronous vibration generally peaks. Suitablefluid for filling the squeeze film cavity 42 is not particularly limitedand can be any fluid that is capable of flow under pressure, such asengine oil.

As shown in the embodiment of FIG. 2, a fluid reservoir 54 is in fluidcommunication with the damper fluid supply line 50 for providing thefluid to the damper fluid supply line 50. The fluid reservoir 54 may bea primary oil supply that collects, filters, and provides oil to variousportions of the apparatus 10, in addition to providing oil to the damperfluid supply line 50. A main supply line 56 is disposed between and influid communication with the fluid reservoir 54 and the damper fluidsupply line 50, and the damper fluid supply line 50 is split from themain supply line 56. The main supply line 56 supplies fluid to portionsof the apparatus 10 beyond the damper fluid supply line 50, and can bedirectly attached to the fluid reservoir 54. In an embodiment, as shownin FIG. 2, a bearing fluid supply line 58 is further split from the mainsupply line 56 for independently providing the fluid to the bearingassembly 16. As also shown in FIG. 2, the main supply line 56 may bemounted to the support housing 26, such as through a flange and boltconnection, with the main supply line 56 including a fluid distributor60 inserted through the support housing 26 and into a space 62 betweenthe anisotropic support 28 and the rotor 14. In this embodiment, thedamper fluid supply line 50 is split from the main supply line 56 in thefluid distributor 60, with the fluid distributor 60 and the supporthousing 26 having complementary portions of the damper fluid supply line50 that align when the fluid distributor 60 is mounted to the supporthousing 26. The bearing fluid supply line 58 extends to a distal end 64of the fluid distributor 60 that is inserted through the support housing26 to provide fluid into the space 62 between the anisotropic support 28and the rotor 14 thereby supplying fluid to the bearing elements 18.

In an embodiment, the fluid is supplied under pressure to the squeezefilm cavity 42 by pressurizing the fluid in the main supply line 56. Inthis embodiment, a fluid pump 66 is disposed in fluid communication withthe main supply line 56 for pressurizing the fluid in the main supplyline 56. The fluid pump 66 thus pressurizes fluid in the main supplyline 56 for supplying fluid under pressure to both the squeeze filmcavity 42 through the damper fluid supply line 50 and the bearingelements 18 through the bearing fluid supply line 58. In an embodiment,the fluid pump 66 is operated to pressurize the fluid in the main supplyline 56 in a range of from about 130 to about 850 KPa.

A fluid interruption device 68 is disposed in the damper fluid supplyline 50, which enables a fluid flow to the squeeze film cavity 42 to beinterrupted without interrupting a fluid flow to the bearing elements 18or any other portion of the apparatus 10. As shown in the embodiment ofFIG. 2, the fluid interruption device 68 is incorporated in the supporthousing 26 and is disposed in the damper fluid supply line 50 within thesupport housing 26, which provides design robustness and enablesconnections between the damper fluid supply line 50 and the fluidinterruption device 68 to be reinforced. However, although not shown, itis to be appreciated that in other embodiments the fluid interruptiondevice 68 may be disposed outside of the support housing 26. Suitablefluid interruption devices 68 include any device that is disposed in thedamper fluid supply line 50 and that interrupts or disrupts the fluidflow to the squeeze film cavity 42. For example, as shown in FIG. 2, thefluid interruption device 68 may halt the fluid flow to the squeeze filmcavity 42 to effectuate interruption of the fluid flow to the squeezefilm cavity 42. Alternatively, although not shown, the fluidinterruption device 68 may release pressure in the damper fluid supplyline 50 to effectuate interruption of the fluid flow to the squeeze filmdamper. For example, the fluid interruption device 68 may reroute thefluid from the damper fluid supply line 50 to other locations within theapparatus 10 to relieve pressure in the damper fluid supply line 50. Inan embodiment, the fluid interruption device 68 includes a pressureregulating valve 68 that functions to interrupt the fluid flow to thesqueeze film cavity 42 through the influence of pressure on an internalpiston (not shown). Alternatively, the fluid interruption device 68 mayinclude a solenoid valve 68. In the embodiment shown in FIG. 2, thefluid interruption device 68 is controlled by an engine control system70, with appropriate sensors (not shown) employed to measure variablesbased upon which a signal can be generated for the fluid interruptiondevice 68 to interrupt the fluid flow to the squeeze film cavity 42.Alternatively, the fluid interruption device 68 may itself be designedto automatically interrupt the fluid flow to the squeeze film cavity 42under certain conditions without the need for controlling by the enginecontrol system 70.

In accordance with the exemplary method, the fluid flow to the squeezefilm cavity 42 is interrupted with the fluid interruption device 68 uponsurpassing a predetermined value of a variable that is correlated torotational speed of the rotor group 12. However, a fluid flow to thebearing assembly 16 is uninterrupted when the fluid flow to the squeezefilm cavity 42 is interrupted, thereby enabling fluid flow to continueto the bearing elements 18. In an embodiment, the variable is furtherdefined as fluid pressure in the damper fluid supply line 50, and thefluid flow to the squeeze film cavity 42 is interrupted by the fluidinterruption device 68 upon surpassing a predetermined value of fluidpressure in the damper fluid supply line 50. In another embodiment, thevariable is further defined as the actual rotational speed of the rotorgroup 12, and the fluid flow to the squeeze film cavity 42 isinterrupted by the fluid interruption device 68 upon surpassing apredetermined value of rotational speed of the rotor group 12. Forexample, because the squeeze film damper is most effective for dampingsynchronous vibration of the rotor group 12 that occurs at the rigidbody critical speed, the predetermined value of the variable maycorrespond to a value of the variable at least at a critical speed ofthe rotor group 12. The fluid flow to the squeeze film cavity 42 isinterrupted upon surpassing the predetermined value of the variable thatis at least at the critical speed of the rotor group 12. Fluid pressurein the damper fluid supply line 50 can be directly correlated torotational speed of the rotor group 12 for purposes of identifying rigidbody critical speeds at which the fluid flow to the squeeze film cavity42 is to be interrupted. In an embodiment, the predetermined value ofthe variable corresponds to a value of the variable in a range of from avalue of the variable at the critical speed of the rotor group 12 to avalue of the variable at about 20 percent above the rigid body criticalspeed of the rotor group 12.

Referring to FIG. 4, simulated results are shown for bearing load whenan apparatus 10 as shown in FIG. 2 is operated in accordance with themethod described above. In particular, the simulated apparatus 10 is agas turbine engine having a rigid body critical speed at about 16,000rpm. Upon traversing the rigid body critical speed and reaching a speedof 20,000 rpm, the fluid flow to the squeeze film cavity 42 is halted,thereby resulting in significantly less bearing loads through theremaining range of operating rotational speeds of the rotor group 12. Inparticular, bearing loads are decreased by at least 30% uponinterrupting the fluid flow to the squeeze film cavity 42, as comparedto a simulation in which the fluid flow to the squeeze film cavity 42 isuninterrupted (as represented in FIG. 1).

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention. It being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims. While at least one exemplary embodimenthas been presented in the foregoing detailed description of theinvention, it should be appreciated that a vast number of variationsexist. It should also be appreciated that the exemplary embodiment orexemplary embodiments are only examples, and are not intended to limitthe scope, applicability, or configuration of the invention in any way.Rather, the foregoing detailed description will provide those skilled inthe art with a convenient road map for implementing an exemplaryembodiment of the invention. It being understood that various changesmay be made in the function and arrangement of elements described in anexemplary embodiment without departing from the scope of the inventionas set forth in the appended claims.

What is claimed is:
 1. An apparatus comprising: a rotor group that isrotatable within the apparatus; a bearing assembly that supports therotor group; a support structure that supports the bearing assembly andthat is fixed in the apparatus, wherein the support structure includes:a support housing; an anisotropic support engaging the bearing assemblyand the support housing; and a squeeze film cavity defined between theanisotropic support and the support housing; a damper fluid supply linein fluid communication with the squeeze film cavity for independentlyproviding a fluid to the squeeze film cavity; and a fluid interruptiondevice disposed in the damper fluid supply line for interrupting a fluidflow to the squeeze film cavity.
 2. The apparatus of claim 1, whereinthe fluid interruption device halts the fluid flow to the squeeze filmcavity upon surpassing a predetermined value of a variable correlated torotational speed of the rotor group.
 3. The apparatus of claim 1,wherein the fluid interruption device comprises a pressure regulatingvalve.
 4. The apparatus of claim 1, wherein the fluid interruptiondevice is controlled by an engine control system.
 5. The apparatus ofclaim 1, wherein a fluid reservoir is in fluid communication with thedamper fluid supply line for providing the fluid to the damper fluidsupply line.
 6. The apparatus of claim 5, wherein a main supply line isdisposed between and in fluid communication with the fluid reservoir andthe damper fluid supply line, and wherein the damper fluid supply lineis split from the main supply line.
 7. The apparatus of claim 6, whereina bearing fluid supply line is further split from the main supply linefor independently providing the fluid to the bearing assembly.
 8. Theapparatus of claim 6, further comprising a fluid pump in fluidcommunication with the main supply line for pressurizing the fluid inthe main supply line.
 9. The apparatus of claim 1, wherein theanisotropic support comprises at least two rings connected byasymmetrically-arranged beams.
 10. The apparatus of claim 9, wherein thesqueeze film cavity is further defined between one of the at least tworings of the anisotropic support and the support housing,
 11. A methodof damping vibration in an apparatus, the method comprising the stepsof: providing the apparatus comprising a rotor group that is rotatablewithin the apparatus, a bearing assembly that supports the rotor group,a support structure that supports the bearing assembly and that is fixedin the apparatus, wherein the support structure includes a supporthousing, an anisotropic support engaging the bearing assembly and thesupport housing, and a squeeze film cavity defined between theanisotropic support and the support housing, and wherein the apparatusfurther comprises a damper fluid supply line in fluid communication withthe squeeze film cavity for independently providing a fluid to thesqueeze film cavity, and a fluid interruption device disposed in thedamper fluid supply line; supplying fluid under pressure to the squeezefilm cavity through the damper fluid supply line; and interrupting afluid flow to the squeeze film cavity with the fluid interruption deviceupon surpassing a predetermined value of a variable correlated torotational speed of the rotor group.
 12. The method of claim 11, whereinthe variable is further defined as fluid pressure in the damper fluidsupply line, and wherein the fluid flow to the squeeze film cavity isinterrupted by the fluid interruption device upon surpassing apredetermined value of fluid pressure in the damper fluid supply line.13. The method of claim 11, wherein the variable is further defined asrotational speed of the rotor group, and wherein the fluid flow to thesqueeze film cavity is interrupted by the fluid interruption device uponsurpassing a predetermined value of rotational speed of the rotor group.14. The method of claim 11, wherein the predetermined value of thevariable corresponds to a value of the variable at least at a criticalspeed of the rotor group, and wherein the fluid flow to the squeeze filmcavity is interrupted upon surpassing the predetermined value of thevariable that is at least at the critical speed of the rotor group. 15.The method of claim 14, wherein the predetermined value of the variablecorresponds to a value of the variable in a range of from a value of thevariable at the critical speed of the rotor group to a value of thevariable at 20 percent above a rigid body critical speed of the rotorgroup.
 16. The method of claim 11, wherein interrupting the fluid flowto the squeeze film cavity comprises halting the fluid flow to thesqueeze film cavity upon surpassing the predetermined value of thevariable correlated to rotational speed of the rotor group.
 17. Themethod of claim 11, wherein a fluid reservoir is in fluid communicationwith the damper fluid supply line through a main supply line disposedbetween and in fluid communication with the fluid reservoir and thedamper fluid supply line, wherein the damper fluid supply line is splitfrom the main supply line, and wherein supplying fluid under pressure tothe squeeze film cavity comprises pressurizing the fluid in the mainsupply line.
 18. The method of claim 17, wherein a bearing fluid supplyline is further split from the main supply line for independentlyproviding the fluid to the bearing assembly, and wherein a fluid flow tothe bearing assembly is uninterrupted when the fluid flow to the squeezefilm cavity is interrupted.
 19. The method of claim 11, wherein bearingloads are decreased by at least 30% upon interrupting the fluid flow tothe squeeze film cavity.
 20. An apparatus comprising: a rotor group thatis rotatable within the apparatus; a bearing assembly that supports therotor group; a support structure that supports the bearing assembly andthat is fixed in the apparatus, wherein the support structure includes:a support housing; an anisotropic support comprising at least two ringsconnected by asymmetrically-arranged beams and engaging the bearingassembly and the support housing; and a squeeze film cavity definedbetween the anisotropic support and the support housing; a damper fluidsupply line in fluid communication with the squeeze film cavity forindependently providing a fluid to the squeeze film cavity; a fluidreservoir in fluid communication with the damper fluid supply line forproviding the fluid to the damper fluid supply line; a main supply linedisposed between and in fluid communication with the fluid reservoir andthe damper fluid supply line, and wherein the damper fluid supply lineis split from the main supply line; a bearing fluid supply line furthersplit from the main supply line for independently providing the fluid tothe bearing assembly; and a fluid interruption device disposed in thedamper fluid supply line and controlled by an engine control system forinterrupting a fluid flow to the squeeze film cavity, wherein a fluidflow to the bearing assembly is uninterrupted when the fluid flow to thesqueeze film cavity is interrupted by the fluid interruption device.